s5 active on tmobile?

My daughter is desperately in need of new phone due to hers got shattered & she lives alone. A friend gave her her att s5 active. I got someone that is unlocking it but I just saw somewhere someone saying the active wont work for web or messages on tmobile. She does live in a city & does travel out of the city. Does Anyone know if itll still work??? Our only other choice are "like new" phones from craigslist that are at least 4-6 yrs old (like the zinger, mytouch, behold II, Samsung gravity Smart, or G-1) - she prefers this 1.
Thank you for any help

I got a Galaxy S5 Active (AT&T G870A) from a trusted user on eBay, it didn't come with a SIM card, as I knew it wouldn't. The device is GSM Unlocked, would I need a AT&T SIM card to switch to T-Mobile? Whenever I enter the devices IMEI on T-Mobile's website, they won't recognize the IMEI, but AT&T IMEI checker works fine.

I got mine on AT&T since it was the closest store to my house and job. The prices online arent even the same when you go instore, I was thinking I was going to be paying $60-$70/month, but im paying $40/month with autopay.